The present invention relates to a welded structural member having a high erosion resistance and, more particularly, to a coating layer formed by build-up welding on the surface of a structural member placed in a flowing fluid, particularly in water flowing at a high flowing velocity, in order to protect the member from erosion caused by a cavitation.
Typical examples of these structural members subjected to erosion are the runners of water turbines for generating electric power, runners of water pumps, ship propellers and so forth. In order to protect such a structural member against the erosion, it is desirable to form the structural member from a material having a high erosion resistance. However, if the whole part of the structural member is formed from such a material having a high erosion resistance, the production cost will be raised uneconomically. To avoid the increase in production cost, it has been proposed to form a protecting layer by a build-up welding on the surface of the structural member.
Stellite is known as one of the materials having a high erosion resistance and suitable for use as a material of build-up welding. In the build-up welding with stellite, however, it is necessary to preheat the material to be built-up up to 200.degree. to 500.degree. C. in order to prevent cracking in the deposited metal, because the stellite is rich in Co, Cr, W and C. The preheating of the material to such a high temperature causes a distortion of the structural member and brings about a high residual tensile stress in the structural member. In addition, the welding work is difficult to conduct in a narrow portion, resulting in a deteriorated weld zone. To avoid this difficulty, it has been proposed to use austenitic stainless steel rods having a high weldability. The austenitic stainless steel, however, has very low erosion resistance as compared with stellite and, therefore, cannot function as an erosion resistant material.
In view of a current tendency that the hydraulic apparatuses are required to operate under more severe condition of use for achieving higher performance, there is an increasing demand for welding material which will facilitate the welding in a narrow portion and which has a sufficiently high erosion resistance.